Date: Thu, 29 Nov 2007 17:36:01 +0000
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: tvrtko.ursulin@sophos.com
Cc: Al Viro <viro@ftp.linux.org.uk>, Casey Schaufler <casey@schaufler-ca.com>,
       Christoph Hellwig <hch@infradead.org>, linux-kernel@vger.kernel.org,
       Valdis.Kletnieks@vt.edu
Subject: Re: Out of tree module using LSM
Message-ID: <20071129173601.34273083@the-village.bc.nu>
In-Reply-To: <OF699E23DA.E36E712D-ON802573A2.00591FA8-802573A2.005A44A2@sophos.com>
References: <20071128183040.GW8181@ftp.linux.org.uk>
	<OF699E23DA.E36E712D-ON802573A2.00591FA8-802573A2.005A44A2@sophos.com>
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> closed. But more importantly further access to it can be blocked until 
> appropriate actions are taken which also applies with your example, no? Is 

That bit is hard- very hard.

> it possible to open for execute and have dirty mappings (or open for 
> write) on a file at the same time?

If I want I can have 16 threads executing code in a shared object being
written to by ten other programs at once and shared over a network while
we are at it. Its probably not a good idea but I can do it if I have
reason to.

Unix and Linux likewise take the basic view that locking is a problem for
the user, while file permissions prevent it being made a problem for
other users.
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